These classes are again subdivided into the direct and alternating current divisions, depending on the character of the current furnished by the magneto. Briefly a continuous current is one that flows continually in one direction while an alternating current periodically reverses its direction of flow. As the alternating current magneto is the most commonly used type, we will confine our description to this class of magneto. The alternating current magneto is much the simplest form of machine as it has no commutator, complicated armature winding, nor field magnet coils, and in some types the brushes and revolving wire are eliminated. As the magnetic flux of an alternating magneto is changed in value, that is increased and decreased, twice per revolution, it follows that the current changes its direction twice for every revolution of the armature. Each change in the direction of current flow is called an alternation. The voltage developed in each alternation or period of flow is not uniform, the voltage being low at the start of the alternation, rapidly increasing in voltage until it is a maximum at the middle, and then rapidly decreasing to zero, from which point the current reverses in direction. As we have two such alternations, in a shuttle type magneto, per revolution we have two points at which the maximum voltage occurs; that is in the center of each alternation. These high voltage points are called the peak of the wave and consequently the sparking devices should operate at the peak of the wave or at the point of highest voltage. The spark therefore should occur when the shuttle or inductors are at a certain fixed point in the revolution at which point the peak of the wave occurs. The peak of the wave occurs when the shuttle is being pulled or turned away from the magnets. In what is known as the “shuttle type” alternating current magneto, the generating coil is wound in the opening of an “H” type armature. This iron armature core is fastened rigidly to the driving shaft and revolves with it. As the armature revolves, it is necessary to collect the current that is generated by means of a brush that slides on a contact button B, the button being connected to one end of the winding. (98) Low Tension Magneto. The winding of the low tension magneto consists of a few turns of very heavy wire or copper strip, one end of which is grounded to the armature shaft and the other passing through the hollow shaft from which it is insulated. The end of the insulated wire is connected to the contact button (B) on which the current collecting brush presses. As one end of the winding is grounded, one brush, and one connecting wire is saved as the current returns to the magneto through the frame of the magneto. As the shuttle revolves between the magnet poles the magnetism is caused to alternate through the iron of the armature, thus causing the current to alternate in direction and fluctuate in value.